In this case, the software glitch affects the car’s cruise control system, and in the words of the recall notice, “in some circumstances the cruise control may not respond to the normal inputs.”
That sounds like a PR-department approved way of saying that the cruise control may not disengage when a customer tells it to, which is a potentially serious defect we’d have a hard time ignoring.
Per the IEEE blog Risk Factor, Jaguar says that no accidents have been reported due to the employee-discovered software problem. Until new code can be written and uploaded to each customer’s car, Jaguar advises customers to “turn off the car’s ignition” if the cruise control won’t disengage.
As Toyota found out with its own stuck accelerator issue, many owners of push button ignition cars don’t even know how to turn off the ignition when the car is moving, since there is no standard method from automobile to automobile. Worse, turning off the ignition will increase steering effort and reduce power assist to the brakes, which the vast majority of drivers have never experienced.
Since the problem appears to be isolated to 2006-10 Jaguar XJ diesel models sold in the UK, customers on this side of the pond need not worry about this particular recall. If you drive a car with a push button ignition, however, it is a good reminder that you should learn the procedure for shutting off your car in an emergency.